The problem of providing improved dispensing, dispersing and dissolving laundry detergent powders is well-known and has been addressed many times in the past. It is undesirable, for example, to have a slow dispensing powder which forms a residue in the drawer of many automatic washing machines. One method of improving the dispensing properties of particulate detergent powders is to include effervescent ingredients.
EP 456 315 (P&G) discloses detergent compositions comprising citric acid and particulate carbonate but no details of the specific grade of carbonate are disclosed.
EP 581 857 (Procter & Gamble) discloses a detergent composition which comprises post dosed sodium carbonate and citric acid where the weight ratio of carbonate to citric acid is from 2:1 to 15:1.
EP 534 525 (Unilever) discloses medium to high bulk density detergent powders comprising carbonate and citric acid whereby more than 80 wt % of the citric acid has a particle size which is in the range of from 350 to 1500 μm. The coarse size of citric acid provides improved moisture stability.
In spite of the moisture stability problem, recent developments have suggested using fine particulate acid source:
WO 98 04662 (Procter & Gamble) discloses a detergent composition comprising effervescent components wherein about 80 wt % of the acid source has a particle size in the range of from 150 μm to about 710 microns with at least 37 wt % of the acid source having a particle size of 350 μm or less.
WO 00 34422 (Procter & Gamble) discloses an effervescent composition comprising an acid source and a carbon dioxide source wherein at least 75% of the acid source has a particle size of from 0.1 to 150 microns; preferably the carbon dioxide source has a volume median particle size of from 5 to 375 microns whereby at least 60% has a particle size of from 1 to 425 microns.